Extend QLData workflow

[AnthonyLim23]

For qldata workflow we should add an option to fix a peak width to a known value (so for a single peak the FWHM is not a free variable, for 2 peaks there is 1 FHWM variable etc.).

will need to update the workflow to use something like this

        func.add_single_lorentzian()
        if func._N_peaks == 1:
            func.set_func_guess(value)
            func.set_func_bounds(lower, upper)
        return func